TITLE:
Ce-SAD Phasing of Glucose Isomerase and Thermolysin Using Cu Kα Radiation
AUTHORS:
Sibi Narayanan, Devadasan Velmurugan
KEYWORDS:
Anomalous Scattering; SAD phasing; Ce; Glucose Isomerase; Thermolysin
JOURNAL NAME:
Crystal Structure Theory and Applications,
Vol.2 No.3,
September
25,
2013
ABSTRACT: Current structural genomics projects aim to solve a large number of
selected protein structures as fast as possible. High degree of automation and
standardization is required at every step of the whole process to speed up
protein structure determination. Phase problem is a bottleneck in
macromolecular structure determination and also in model building which is a
time-consuming task. The simplest approach to phasing macromolecular crystal
structures is the use of a SAD signal. SAD data can be collected using the
in-house copper (1.54 A) wavelength source. Data collected using copper
wavelength with the incorporation of anomalously scattering heavy metal atoms
may serve as a powerful tool for structural biologists to solve novel protein
structures as well where synchrotron beam line is not available. A short soak
of protein crystals in heavy metal solution or by incorporating heavy atoms
into the protein drop while crystallizing the protein (co-crystallization)
leads to incorporation of these heavy metal ions into the ordered solvent shell
around the protein surface. The present work aims to determine whether cerium
ion can be successfully incorporated into the protein crystal through
quick-soaking method while maintaining the isomorphism. The study also aims in
understanding whether this metal ion can be used for phasing purpose. The
intensity data are collected and analyzed for anomalous signal, substructure solution
and the binding sites.